Really leave it alone.Let it handle things by itself. It will do it itself. You cannot be smarter than Android when it comes to android. Don't Micromanage stuffs.

Do not Use Smart Manager Features on your device

Do not Swipe away apps from recent screens except games.

Do not Force Stop Apps (except some Games)

Do not Disable Bloatware but avoid using it (Pre-installed apps)

Auto Reboot Every Monday at 3 a.m.

Do not Download 3rd Party Apps like Du Battery Saver , they will just kill apps prematurely.

Restarts Kill Battery

Any android app , that runs on your phone needs memory. Memory or RAM is essentially limited . OnePlus Three or The New Galaxy Note 7 might have more RAM. But still it is limited . Sooner or later the app that you ran will be closed when other app needs more RAM. The issue here is that a Full RAM will not take any more battery than when the app is removed from memory and needs to be restarted again. That 'restart' is the real Mother Battery Killer.